Automatically resettable circuit breaker system



Nov. 27, 1956 A. J. SCHULTZ 2,772,379

AUTOMATICALLY RESETTABLE CIRCUIT BREAKER SYSTEM Filed July 9, 1953 INVENTOR AR THUR d. SCHULTZ ATTORNEY United States Patent AUTOMATICALLY RESETTABLE CIRCUIT BREAKER SYSTEM Arthur J. Schultz, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application July 9, 1953, Serial No. 366,945

3 Claims. (Cl. 31723) This invention relates to circuit breakers of the electronic type.

It is an object of the invention to provide an automatically operable electronic circuit breaker which shall open at or above a predetermined current flow through a load.

It is a still further object of the invention to make the circuit breaker in such fashion that it will automatically reclose on the diminishing of the current flow through the load but only if the current drops to a desired low level.

These and other objects of the invention will become apparent after reading the following specification and claims in the light of the accompanying drawing in which the single figure is a diagram of a circuit embodying my invention Considering the drawing more in detail, there is illustrated a Wheatstone bridge comprising a pair of triodes and 12, the plate circuits of which form two arms of the bridge and a pair of resistors 14 and 16 which form the other two arms of the bridge. The resistors at their one ends are connected to a positive source of D. C. potential and at their other ends are connected respectively to the anodes 18 and 20 of the triodes. The cathodes 22 and 24 of the triodes are connected together and lead to the other or negative side of the source of D. C. potential through a common cathode resistor 26. The bridge sensing element is an electromagnetic circuit breaker whose coil 28 connects the two anodes of the triodes. A steadying condenser 30 spans the coil to prevent transients from affecting the operation of the circuit breaker. The circuit breaker further comprises an armature 32 which, when the coil is insufficiently energized, contacts back contact 34 and which armature, when the coil is sufficiently energized, contacts from contact 36. The armature is connected with the positive side of the D. C. source of potential via an indicating instrument such as a milliameter 38.

Connected across the D. C. line is a string of resistors 40, 42 and 44, the resistor 44 being in the form of a potentiometer. The junction 46 between resistors 40 and 42 is connected to the grid 48 of triode 10.

A second pair of resistors 50 and 52 is also strung across the line and the junction 54 between these resistors is connected to a potentiometer 56 and thence to the grid 58 of triode 12.

The normally closed back contact 34 of the circuit breaker is connected to a load 60, the current through which is to be controlled, and from the load 60 there is a line 62 leading to a junction 64 between resistance 42 and potentiometer 44. A circuit to indicate an overload condition is provided this circuit being controlled by current flow in the coil 28. This circuit comprises a line 64 connecting the normally open front contact 36 to an indicator, such as a neon lamp 66 with its protective resistor 68. The resistor or opposite side of the indicator is connected to the negative side of the line.

interposed between the potentiometer 56 and a junc- ICC tion point 70 on the line 71 joining contact 34 and the load 60 is a diode 72 whose anode is connected to the potentiometer and whose cathode is connected to the junction point 70.

During normal operation, current flows from the positive side of the D. C. potential source, through the switch contact 34, the line 71, load 60, potentiometer 44 and back to the D. C. source. Both triodes 10 and 12 are conductive since the values of the potential dividers 40, 42, 44 and 50, 52 are selected to impose low positive potential on the grids 48 and 58. The cathode resistor 26 automatically maintains the correct grid bias on the triodes. The potentiometer 44 adjusts the bias on triode 10 to facilitate establishing current flow through the triode at a desired level such as to initially establish a balanced bridge condition.

Therefore, the bridge, under normal operative loads, is substantially balanced. With increase of load, i. c. with decrease of load resistance, the voltage at point 64 rises, creating a smaller potential drop across the resistors 40 and 42 which are parallel with the load, and point 46 becomes more positive resulting in an increase in the current flow in triode 10 and an upsetting of the balance of the bridge. Since the resistors 50 and 52 are directly across the line and do not bridge the same points as resistors 40 and 42, the potential drop across them is not afiected in the same way, the potential at point 54 varying very little compared to the variation at point 46. If the bridge be sufficiently upset, the coil 28 will be energized sulficiently to attract the armature 32 and open the load circuit. At this time another circuit takes over preventing resetting of the circuit breaker until the overload is removed. This is eifected in the following manner:

When no overload exists, the potential at point 54 between the resistors 50 and 52 is substantially lower than that which exists at point 70. The anode of diode 72 is therefore at lower potential than the cathode and no current flows through the diode. The potential at the grid 58 of triode 12 is therefore that which exists at the junction point 54 since at this time there is no current flow through the potentiometer 56.

With an overload condition, the armature 32 is attracted and the contact 34 is opened whereby the cathode of the diode 72 is no longer under high positive poten tial. The diode now becomes conductive and a current of smaller magnitude flows through a shunt circuit around contact 34, this shunt circuit including resistor 50, potentiometer 56, diode 72, load 60, line 62, and potentiometer 44, causing the grid 58 of triode 12 to become less positive than before and thereby maintaining the unbalanced condition of the bridge, notwithstanding the drop in voltage occurring at junction 46 and grid 48 when the contact 34 was opened.

As the contact 34 is opened, the contact 36 is closed thereby establishing the signal circuit through the neon lamp 66.

So long as a low resistance condition of the load eX- ists, considerable current will flow through the load via potentiometer 56, maintaining the potential at grid 58 at a comparatively low value. When the low resistance condition of the load rights itself or is removed, the current flow through the potentiometer 56, diode 72 and load 60 diminishes, the potential on the grid 58 rises and the bridge approaches a sufficiently close balance to allow the armature 32 to move into contact with back contact 34, thereby automatically reestablishing the load circuit, ready for repeat operation of the circuit breaker should an overload occur again.

The potentiometer 44 is utilized to attain better bridge balance as stated heretofore, while the potentiometer 56 is utilized to vary the response of restoration of the bridge with respect to magnitude of current flow in the load WlTfi the contact 34 is open.

Obviously many changes may be made in the circuit of my invention so long as they do not depart from the spirit of the invention as defined in the appended claims. Thus, the two triodes may Be in a single envelope, the millia'r'ne'ter may be replaced by another form of indicating instrument or be dispensed with altogether and the same applies to the neon indicator; the Whe'atstone bridge may be replaced by a Wein bridge or other form of idge- 'What'i's claimed is:

1. An automatically resettable overload circuit breaker arrangement comprising a Wheatstone bridge connected across asource of potential, two arms of the bridge being triodes, a common biasing resistor in the cathode circuits of the tri'odes, a magnetic coil across the arms for sensing b'rid'ge unbalance, a circuit breaker connected to a source of potential and operated by said coil, a series arrangement of a pair of resistors and a potentiometer, all in parallel arrangement with respect to the bridge, a conneetion between the grid of one triode and a point between the resistors of the pair, a second series arrangement of a pair of resistors in parallel with the bridge, a second potentiometer connecting the grid of the other of said tri'odes with a point between the resistors of said second series arrangement, a load connected between the circuit breaker and a point between the juncture of the first potentiometer and resistor of the first pair, and a diode with its anode connected to the grid of the second trio'de and its cathode to a point between the circuit breaker and load.

2. An automatically resettable overload circuit breaker arrangement comprising a Wheatstone bridge connected across a source of potential, two arms of the bridge being triodes", a common biasing resistor in the cathode circuits of the triod'es, a magnetic coil across the arms for sensing bridge unbalance, a circuit breaker connected to a source of potential operated by said coil, a condenser shunting said coil, a series arrangement of a pair of resistors and a potentiometer, all in parallel arrangement with respect to the bridge, a connection between the grid of one triode and a point between the resistors of the pair, a second series arrangement of a pair of resistors in parallel with the bridge, a second potentiometer conmeeting the grid of the other of said triodes with a point between the resistors of said second series arrangement, a load connected between the circuit breaker and a point between the juncture of the first potentiometer and resistor of the first pair, and a diode with its anode connected to the grid of the second triode and its cathode to a point between the circuit breaker and load.

3. An automatically reset'tableoverload circuit breaker arrangement comprising a bridge consisting of four voltage dropping arms to, in efiect, form a diamond with a voltage source connected between one pair of opposite junctions of the diamond and a voltage difierence sensing device connected between the opposite pair of junctions of the diamond, a Circuit breaker, load, and resistor in series relation and connected across a source of potential, said circuit breaker being connected to the voltage diflerence sensing device of the bridge to be operated thereby, two of said voltage dropping arms of the bridge being variable, means for varying the voltage drop across one of said variable voltage dropping arms comprising a voltage sensitive device and a first conductor between said voltage sensitive device and the junction between the load and the resistor, a second conductor leading to said voltage sensitive device and including a resistor connected to the source of potential applied to the bridge, means for varying the voltage drop across the other of said variable voltage dropping arms comprising a second voltage sensitive device, a pair of resistors in series with each other and parallel to the bridge and across the source of potential applied to the bridge, a tap between the pair of resistors and leading to the second voltage sensitive device, a third conductor between the tap and a point between the circuit breaker and the load, and a third voltage sensitive devicein' that third conductor tocomplete or disrupt current flow through said third conductor.

References Cited in the file of this patent UNITED STATES PATENTS 1,567,017 Traver Dec. 22, 1925 1,610,590 Reagan Dec. 14, 1926 2,259,965 Ta'liaferro Oct. 21, 1941 

